1. Field of the Invention
The present invention relates to the separation of vital wheat gluten and starch and, more particularly, to a wet process for fractionating vital wheat gluten, starch and bran-germ from the whole wheat kernel with minimum damage to the functional, chemical and biological characteristics of the wheat kernel components.
2. Description of the Prior Art
The milling of wheat can basically be divided into two categories: (1) dry milling and (2) wet milling with aqueous solvents. Dry milling of wheat is a familiar process which produces patent wheat flour, second clears (lower quality flour), various other low grade flour products, bran, and germ. The products designated as flour are those obtained from the endosperm which contains the wheat starch and gluten. It is not presently possible to efficiently separate the starch and gluten contained in the endosperm by dry milling techniques.
The commercial production of vital wheat gluten and the separation of starch therefrom has been accomplished in the past by wet milling techniques using wheat flour or second clears (a small fraction of the flour stream) as the starting material by the "dough ball" process and modifications thereof, which processes essentially separate the wheat starch from the gluten protein. In one process, the gluten is maintained as a single coherent mass and the starch is washed out of a flour and water dough. Another process disperses the dough in water and recovers the gluten particles on a screen. Variations of the basic dough ball process utilizing wheat flour account for a major part of the vital gluten produced commercially today. Until recently, no known gluten production process employed the whole wheat kernel as the starting material. This was probably because production of vital wheat gluten is a comparatively recent innovation which developed from starch recovery processes. Early starch recovery processes utilized the whole wheat kernel but could not be converted to gluten production because the process conditions were too harsh and destroyed or devitalized the gluten. On the other hand, dough ball or batter processing from wheat flour was relatively simple because the bran and the germ had been substantially removed in the milling process. In addition, high ash second clears worked well in the dough ball process and were available at attractive prices as a by-product of the flour milling industry. Consequently, wheat gluten processing had been flour oriented for decades and no need had apparently existed to motivate the development of a process starting from the whole wheat kernel. However, improvements in milling techniques coupled with a drastic decline in the number of operative flour mills has led to current shortages of and higher prices for clears. As a result, millions of pounds of vital wheat gluten are imported by the United States each year to meet demands domestic producers cannot fill.
Processes for vital wheat gluten-starch separation and gluten recovery which utilize the whole wheat kernel as the starting material are taught in U.S. Pat. No. 3,891,613 and U.S. Pat. No. 3,979,375. According to these processes the whole wheat kernel is tempered in water and impact milled or flaked. The resulting particles or flakes are thereafter hydrated to saturation to form a thick, dough-like mass and mechanically worked in the presence of water to wash the wheat kernel components from the gluten. Other patents which disclose wet milling fractionation of the whole wheat kernel include U.S. Pat. Nos. 3,790,553, 3,788,861, 3,832,472, 3,851,085, 3,857,987, 3,868,355 and 3,958,016.
Complete dough hydration as a preliminary to component fractionation is taught in all these patents and has always been considered an essential element in the effective separation and recovery of high quality wheat components in high yields. The better the hydration, it has been found, the better are the yields of the wheat endosperm components, starch and gluten. Therefore, it has been a goal of wet milling processes to improve the rate and extent of hydration to improve these yields. However, efforts to improve hydration to increase yields, e.g., by reducing particle sizes, are generally inconsistent and at cross purposes with efforts to improve the quality of the fractions and to separate and recover bran-germ.